In the related art, molded articles manufactured by injection-molding of resin materials are applicable to products with a high degree of flexibility and thus have been widely used for automobile parts, electrical appliance parts, and other articles for daily use. However, molded articles only made of general-purpose resin materials disadvantageously have low mechanical strength.
For this reason, in some cases, a fibrous filler is used as a material added in order to reinforce general-purpose resin materials. The fibrous filler includes, for example, a glass fiber, a carbon fiber, or a natural fiber. These fibrous fillers have extremely high tensile strength and thus are mixed with general-purpose resin materials to prepare composite resin materials. This can improve the mechanical strength of molded articles or reduce the weights of molded articles.
Materials used as fibrous fillers include a cellulose fiber, a kind of natural fibers. Cellulose fibers can be manufactured using wood and thus are expected to be highly available at low cost. Moreover, cellulose fibers can be easily treated after disposal and can be properly recycled, leading to a light environmental load.
If cellulose fibers are used as filler, ensuring sufficient strength requires a fiber disentangling step in which fibers are finely disentangled from materials such as wood pulp, and a step of dispersing fibers into a resin material. In the dispersing step, unfortunately, cellulose fibers with a hydrophilic base are difficult to disperse in a resin material.
Thus, in JP2012-102324A, a specific disperser is mixed in a resin material and cellulose fibers, thereby properly dispersing the cellulose fibers. The disperser contains a disperser having a hydroxyl value of at least 30 mgKOH/g. The disperser preferably has a concentration of 2 to 10 mass %. With this configuration, cellulose fibers are properly dispersed into a resin material, achieving a molded article with high mechanical strength, e.g., high tensile strength or a high bending modulus. Furthermore, with this configuration, an injection-molded article can be obtained with high injection moldability and a proper external appearance.